1. Field of the Invention
The invention to which the present application pertains relates to float valves useful in connection with oil well cementing operations and in particular relates to float valves which are suitable for use in connection with float shoes, float collars and the like adapted for sub-surface cementing operations. Even more particularly, the device of the invention to which the present application pertains may be used to prevent the flow of fluid in an upward direction through the float collar or float shoe as a casing string is lowered into a well and to permit the flow of fluid in a downward direction through the casing during the cementing operation.
2. Description of the Prior Art
Float collars and shoes are devices which are well-known in the art to which the present invention pertains. These devices are used extensively in casing running and cementing operations in the downhole well bore. Shoes and collars may also be run on conductor casing, protection strings, intermediate strings and liners, in addition to production casing. After a well has been drilled to below the oil production layer, or strata, what is termed "production casing" may be run down inside the well bore to the bottom. Initially, the well bore is typically filled with a mixture of water, oil, drilling mud, etc. and it is desirable that such fluid mixtures do not enter the production casing as the latter is lowered into position within the well bore. To effect this, a guide shoe or float shoe device is attached to the first length of casing to be lowered into the well bore. Such shoes often have rounded noses to guide the casing around obstructions, ledges, etc. within the well bore.
The float collar or float shoe incorporates an internal float valve assembly in the nature of a check valve or one-way valve which prevents flow of the various fluids in the well upwardly into the casing string but which are capable of opening to permit pumping of cement downwardly during the cementing operation. Float valves are subject to extreme abrasive conditions during the cementing operation. Additionally, such valves must be capable of withstanding very high differential pressures during the lowering of the string to prevent backflow of the well fluids into the string as the same is lowered. The float valve assembly of the present invention incorporates design features which minimize damage from abrasion and at the same time provide maximum sealing characteristics to prevent backflow of well fluid.